1. Field of the Invention
The present invention relates generally to electrical connectors for coaxial cables and related electrical fittings. More particularly, the present invention relates to coaxial F-connectors of the axial compression type which are adapted to be installed with hand compression tools, and specifically to F connectors that are internally sealed when compressed. Known prior art of relevance is classified in U.S. patent No. Class 439, Subclasses 349, 583, and 584.
2. Description of the Related Art
A variety of coaxial cable connectors have been developed in the electronic arts for interfacing coaxial cable with various fittings. Famous older designs that are well known in the art, such as the Amphenol PL-259 plug, require soldering and the hand manipulation of certain components during installation. One advantage of the venerable PL-259 includes the adaptability for both coaxial cables of relatively small diameter, such as RG-59U or RG-58U, and large diameter coaxial cable (i.e., such as RG-8U, RG-9U, LMR-400 etc.). So-called N-connectors also require soldering, but exhibit high frequency advantages. Numerous known connectors are ideal for smaller diameter coaxial cable, such as RG-58U and RG-59U. Examples of the latter include the venerable “RCA connector”, which also requires soldering, and the well known “BNC connector”, famous for its “bayonet connection”, that also requires soldering with some designs.
Conventional coaxial cables typically comprise a solid or stranded center conductor surrounded by a plastic, dielectric insulator and a coaxial shield of braided copper and foil. An outer layer of insulation, usually black in color, coaxially surrounds the cable. To prepare coaxial cable for connector installation, a small length of the jacket is removed, exposing a portion of the outer conductive shield that is drawn back and coaxially positioned. A portion of the insulated center is stripped so that an exposed portion of the inner copper conductor can become the male prong of the assembled F-connector. Experienced installers are well versed in the requirements for making a “prepared end” of a coaxial line for subsequent attachment to a compression F-connector.
The modern F-type coaxial cable connector has surpassed all other coaxial connector types in volume. These connectors are typically used in conjunction with smaller diameter coaxial cable, particularly RG-6 cable and the like. The demand for home and business wiring of cable TV system, home satellite systems, and satellite receiving antenna installations has greatly accelerated the use of low-power F-connectors. Typical F-connectors comprise multiple pieces. Typically, a threaded, hex-head nut screws into a suitable socket commonly installed on conventional electronic devices such as televisions, satellite receivers and accessories, satellite radios, and computer components and peripherals. The connector body mounts an inner, generally cylindrical post that extends coaxially rearwardly from the hex nut. Usually the post is barbed.
When a prepared end of the coaxial cable is inserted, the post penetrates the cable, sandwiching itself between the insulated cable center and the outer conductive braid. A deflectable, rear locking part secures the cable within the body of the connector after compression. The locking part is known by various terms in the art, including “cap”, or “bell” or “collar” or “end sleeve” and the like. The end cap, which may be formed of metal or a resilient plastic, is compressed over or within the connector body to complete the connection. A seal is internally established by one or more O-rings or grommets. Suitable grommets may comprise silicone elastomer.
The design of modern F-connectors is advantageous. First, typical assembly and installation of many F-connector designs is completely solderless. As a result, installation speed increases. Further, typical F-connectors are designed to insure good electrical contact between components. The outer conductive braid for the coaxial cable, for example, is received within the F-connector, and frictional and/or compressive contact insures electrical continuity. For satellite and cable installations the desired F-connector design mechanically routes the inner, copper conductor of the coaxial cable through the connector body and coaxially out through the mouth of the connector nut to electrically function as the male portion of the connector junction without a separate part.
An important F-connector design innovation relates to the “compression-type” F-connector. Such designs typically comprise a metallic body pivoted to a hex-head nut for electrical and mechanical interconnection with a suitably threaded socket. A rigid, conductive post is coaxially disposed within the connector body, and is adapted to contact the conductive outer braid of the coaxial cable when the prepared cable end is installed. After insertion of the stripped end of the coax, the rear connector cap or collar is forcibly, axially compressed relative to the connector body. A suitable hand operated compression tool designed for compression F-connectors is desirable. Some connector designs have an end cap adapted to externally mount the body, and some designs use a rear cap that internally engages the F-connector body. In some designs the cap is metal, and in others it is plastic. In any event, after the cap is compressed, the braided shield in electrically connected and mechanically secured, and a tip of the exposed copper center conductor properly extends from the connector front. The conductive metallic coaxial cable braid compressively abuts internal metal components, such as the post, to insure proper electrical connections.
One popular modern trend with compression F-connectors involves their preassembly and packaging. In some preassembled designs the rear sleeve (i.e., or end cap, collar etc.) is compressively forced part-way unto or into the connector body prior to bulk packaging. The end sleeve is pre-connected to the connector end by the manufacturer to ease the job of the installer by minimizing or avoiding installation assembly steps. For example, when the installer reaches into his or her package of connectors, he or she need draw out only one part, or connector, and need not sort connector bodies from connector end caps or sleeves and assemble them in the field, since the device end cap is already positioned by the manufacturer. Because of the latter factors, installation speed is increased, and component complexity is reduced.
Typically, preassembled compression F-connector designs involve locking “detents” that establish two substantially fixed positions for the end cap along the length of the connector body. The cap, for example, may be provided with an internal lip that surmounts one or more annular ridges or grooves defined on the connector collar for the mechanical detent. In the first detent position, for example, the end cap yieldably assumes a first semi-fixed position coupled to the lip on the connector end, where it semi-permanently remains until use and installation. The connection force is sufficient to yieldably maintain the end cap in place as the F-connectors are manipulated and jostled about. During assembly, once a prepared cable end is forced through the connector and its end cap, the connector is placed within a preconfigured void within and between the jaws of a hand-operated compression installation tool, the handles of which can be squeezed to force the connector parts together. During compression, in detented designs, the end cap will be axially forced from the first detent position to a second, compressed and “installed” detent position.
High quality F-connectors are subject to demanding standards and requirements. Modern home satellite systems distribute an extremely wide band signal, and as the demand for high definition television signals increases, and as more and more channels are added, the bandwidth requirements are becoming even more demanding. At present, a goal in the industry is for F-connectors to reliably handle bandwidths approximating three to four GHz.
Disadvantages with prior art coaxial F-connectors are recognized. For example, moisture and humidity can interfere with electrical contact, degrading the signal pathway between the coax, the connector, and the fitting to which it is connected. For example, F-connectors use compression and friction to establish a good electrical connection between the braided shield of the coaxial cable and the connector body, as there is no soldering. Moisture infiltration, usually between the connector body and portions of the coaxial cable, can be detrimental. Signal degradation, impedance mismatching, and signal loss can increase over time with subsequent corrosion. Moisture infiltration often increases in response to mechanical imperfections resulting where coaxial compression connectors are improperly compressed.
Mechanical flaws caused by improper crimping or compression can also degrade the impedance or characteristic bandwidth of the connector, attenuating and degrading the required wide-band signal that modern TV satellite dish type receiving systems employ. If the axial compression step does not positively lock the end cap in a proper coaxial position, the end cap can shift and the integrity of the connection can suffer. Furthermore, particularly in modern, high-bandwidth, high-frequency applications involved with modern satellite applications distributing multiple high definition television channels, it is thought that radial deformation of internal coaxial parts, which is a natural consequence of radial compression F-connectors, potentially degrades performance.
Dealers and installers of satellite television equipment have created a substantial demand for stripping and installation tools for modern compression type F-connectors. However, installers typically minimize the weight and quantity of tools and connectors they carry on the job. There are a variety of differently sized and configured F-connectors, and a variety of different compression tools for installation.
On the one hand, F-connectors share the same basic shape and dimensions, as their connecting nut must mate with a standard thread, and the internal diameter of critical parts must accommodate standard coaxial cable. On the other hand, some compression F connectors jam the end sleeve or cap into the body, and some force it externally. Some connectors use a detent system, as mentioned above, to yieldably hold the end sleeve or cap in at least a first temporary position. Still other connectors require manual assembly of the end cap to the body of the connector. In other words, size differences exist in the field between the dimensions of different F-connectors, and the tools used to install them.
The typical installer carries as few tools as practicable while on the job. He or she may possess numerous different types of connectors. Particularly with the popularity of the “detented” type of compression F-connector, hand tools customized for specific connector dimensions have arisen. The internal compression volume of the hand tool must match very specific “before” and “after” dimensions of the connector for a precision fit. After a given compression F-connector is preassembled, then penetrated by the prepared end of a segment of coaxial cable, the tool must receive and properly “capture” the connector. The most popular compression tools are known as “saddle” types, or “fully enclosed” types. In either event the tool must be sized to comfortably receive and “capture” connectors of predetermined external dimensions. Tools are designed for proper compression deflection, so the connector assumes a correct, reduced length after compression. Popular tools known in the art are available from the Ripley Company, model ‘Universal FX’, the ‘LCCT-1’ made by International Communications, or the ICM ‘VT200’ made by the PPC Company.
Connector failures often result from small mechanical misalignments that result where the internal compression volume of the installation tool does not properly match the size of the captured connector. The degree of internal tool compression should closely correlate with the reduced length of the connector after axial deflection. In other words, the end sleeve or cap must be forcibly displaced a correct distance. Wear and tear over time can mismatch components. In other words, where hand tools designed for a specific connector length are used with connectors of slightly varying sizes, as would be encountered with different types or brands of connectors, improper and incomplete closure may result. Misdirected compression forces exerted upon the end cap or sleeve and the connector body or during compression can cause deformation and interfere with alignment. The asymmetric forces applied by a worn or mismatched saddle type compression tool can be particularly detrimental. Sometimes improper contact with internal grommets or O-rings results, affecting the moisture seal.
The chance that a given compression hand tool, used by a given installer, will mismatch the particular connectors in use at a given time is often increased when the connectors are of the “detent” type. Detented compression connectors, examples of which are discussed below, are designed to assume a predetermined length after both preassembly, and assembly. Thus detented F-connectors require a substantially mating compression tool of critical dimensions for proper performance. The chances that a given installer will install the requested compression F-connectors involved at a given job, or specified in a given installation contract, with the correctly sized, mating installation tool are less than perfect in reality. Another problem is that detented F-connector, even if sized correctly and matched with the correct installation tool, may not install properly unless the installer always exerts the right force by fully deflecting the tool handles. Even if a given installation tool is designed for the precise dimensions of the connectors chosen for a given job, wear and tear over the life of the hand tool can degrade its working dimensions and tolerances. Real world variables like these can conclude with an incorrectly installed connector that does not reach its intended or predetermined length after assembly.
If and when the chosen compression tool is not correctly matched to the F-connector, deformation and damage can occur during installation, particularly with detented compression F-connectors. Another problem occurs where an installer improperly positions the connector within the hand tool. Experienced installers, who may have configured and installed thousands of F-connectors over the years, often rely upon a combination of “look” and “feel” during installation when fitting connectors to the cable, and when positioning the connectors in the hand tool. Repetition and lack of attention tends to breed sloppiness and carelessness. Improper alignment and connector placement that can cause axial deformation. Sloppiness in preparing a cable end for the connector can also be detrimental.
A modern, compression type F-connector of the compression type is illustrated in U.S. Pat. No. 4,834,675 issued May 30, 1989 and entitled “Snap-n-seal Coaxial Connector.” The connector has an annular compression sleeve, an annular collar which peripherally engages the jacket of a coaxial cable, an internal post coaxially disposed within the collar that engages the cable shield, and a rotatable nut at the front for connection. A displaceable rear cap is frangibly attached to the body front, and must be broken away for connector installation manually and then pre-positioned by the user on the connector end. The end cap is axially forced into coaxial engagement within the tubular compression sleeve between the jacket of the coaxial cable and the annular collar, establishing mechanical and electrical engagement between the connector body and the coaxial cable shield.
U.S. Pat. No. 5,632,651 issued May 27, 1997 and entitled “Radial compression type Coaxial Cable end Connector” shows a compression type coaxial cable end connector with an internal tubular inner post and an outer collar that cooperates in a radially spaced relationship with the inner post to define an annular chamber with a rear opening. A threaded head attaches the connector to a system component. A tubular locking cap protruding axially into the annular chamber through its rear is detented to the connector body and is displaceable axially between an open position accommodating insertion of the tubular inner post into a prepared cable end, with an annular outer portion of the cable being received in the annular chamber, and a clamped position fixing the annular cable portion within the chamber.
Similarly, U.S. Pat. No. 6,767,247 issued Jul. 27, 2004 depicts a compression F-connector of the detent type. A detachable rear cap or end sleeve temporarily snap fits or detents to a first yieldable position on the connector rear. This facilitates handling by the installer. The detachable end sleeve coaxially, penetrates the connector body when installed, and the coaxial cable shield is compressed between the internal connector post and the end sleeve.
U.S. Pat. No. 6,530,807 issued Mar. 11, 2003, and entitled “Coaxial connector having detachable Locking Sleeve,” illustrates another modern compression F-connector. The connector includes a locking end cap provided in detachable, re-attachable snap engagement within the rear end of the connector body for securing the cable. The cable may be terminated to the connector by inserting the cable into the locking sleeve or the locking sleeve may be detachably removed from the connector body and the cable inserted directly into the cable body with the locking sleeve detached subsequently.
U.S. Pat. No. 5,470,257 issued Nov. 28, 1995 shows a detented, compression type coaxial cable connector. A tubular inner post is surrounded by an outer collar and linked to a hex head. The radially spaced relationship between the post and the collar defines an annular chamber into which a tubular locking cap protrudes, being detented in a first position that retains it attached to the connector. After the tubular inner post receives a prepared cable end, the shield locates within the annular chamber, and compression of the locking cap frictionally binds the parts together.
U.S. Pat. No. 6,153,830 issued Nov. 28, 2000 shows a compression F-connector with an internal post member, and a rear end cap that coaxially mounts over the cable collar or intermediate body portion. The internal, annular cavity coaxially formed between the post and the connector body is occupied by the outer conductive braid of the coaxial cable. The fastener member, in a pre-installed first configuration is movably fastened onto the connector body. The fastener member can be moved toward the nut into a second configuration in which the fastener member coacts with the connector body so that the connector sealingly grips the coaxial cable. U.S. Pat. No. 6,558,194 issued May 6, 2003 and entitled “Connector and method of Operation” and U.S. Pat. No. 6,780,052 issued Aug. 24, 2004 are similar.
U.S. Pat. No. 6,848,940 issued Feb. 1, 2005 shows a compression F-connector similar to the foregoing, but the compressible end cap coaxially mounts on the outside of the body.
Another detented compression F-connector is discussed in U.S. Pat. No. 6,848,940, issued Feb. 1, 2005 and entitled “Connector and method of Operation.” The connector body coaxially houses an internal post that is coupled to the inner conductor of a coaxial cable. A nut is coupled to either the connector body or the post for the connecting to a device. The post has a cavity that accepts the center conductor and insulator core of a coaxial cable. The annulus between the connector body and the post locates the coaxial cable braid. The end cap or sleeve assumes a pre-installed first configuration temporarily but movably fastened to the connector body, a position assumed prior to compression and installation. The end cap can be axially forced toward the nut into an installed or compressed configuration in which it grips the coaxial cable.
Various hand tools that can crimp or compress F-connectors are known.
For example, U.S. Pat. No. 5,647,119 issued Jul. 15, 1997 and entitled “Cable terminating Tool” discloses a hand tool for compression type F-connectors. Pistol grip handles are pivotally displaceable. A pair of cable retainers pivotally supported on a tool holder carried by one of the handles releasably retains the cable end and a preattached connector in coaxial alignment with an axially moveable plunger. The plunger axially compresses the connector in response to handle deflection. The plunger is adjustable to adapt the tool to apply compression type connector fittings produced by various connector manufactures.
Another example is U.S. Pat. No. 6,708,396 issued Mar. 23, 2004 that discloses a hand-held tool for compressively installing F-connectors on coaxial cable. An elongated body has an end stop and a plunger controlled by a lever arm which forcibly, axially advances the plunger toward and away from the end stop to radially compress a portion of the connector into firm crimping engagement with the end of the coaxial cable.
Similarly, U.S. Pat. No. 6,293,004 issued Sep. 25, 2001 entitled “Lengthwise compliant crimping Tool” includes an elongated body and a lever arm which is pivoted at one end to the body to actuate a plunger having a die portion into which a coaxial cable end can be inserted. When the lever arm is squeezed, resulting axial plunger movements force a preassembled crimping ring on each connector to radially compress each connector into sealed engagement with the cable end, the biasing member will compensate for differences in length of said connectors.
Despite numerous attempts to improve F-connectors, as evidenced in part by the large number of existing patents related to such connectors, a substantial problem with internal sealing still exists. It is important to prevent the entrance of moisture or dust and debris after the connector is installed. To avoid degradation in the direct current signal path established through the installed connector's metal parts, and the radio frequency, VHF, UHF and SHF signal paths and characteristics, a viable seal is required. Connectors are commonly used with coaxial cables of several moderately different outside diameters. For example, common RG-59 or RG-59/U coaxial cable has a different diameter than RG-6 or RG-6/U coaxial cable. Some cables have differently sized outer jackets and other internal differences that may not be readily apparent to the human eye. One way to promote sealing is through internal grommets or seals that are deflected and deformed when the fitting is compressively deployed to tightly encircle the captivated coaxial cable.
For example, U.S. Pat. No. 3,678,446 issued to Siebelist on Jul. 18, 1972 discloses an analogous coaxial connector for coaxial cables which have different sizes and structural details. An internal, coaxial sealing band is utilized for grasping the coaxial cable when the connector parts are secured together. Other examples of connectors or analogous electrical fittings with internal sealing grommets include U.S. Pat. Nos. 3,199,061, 3,375,485, 3,668,612, 3,671,926, 3,846,738, 3,879,102, 3,976,352, 3,986,737, 4,648,684, 5,342,096, 4,698,028, 6,767,248, 6,805,584, 7,118,416, and 7,364,462. Also pertinent are foreign references WO/1999065117, WO/1999065118, WO/2003096484 and WO/2005083845.
The sealing problem associated with compressive F-connectors discussed above, however, remains a difficult problem to overcome and is a focus of this invention. Moreover, during experiments with compression F-connectors of the type discussed above, it has been suggested that the conventional barbed post utilized in many designs creates signal discontinuities and degrades bandwidth. For example, the conical geometry of the barbs necessitates that such posts vary in diameter. It is thought that at extremely high frequencies this creates passive intermodulation. Barbed posts with barbs varying in diameter from their shank can create abutting resonate cavities at very high frequencies. As a result, the achievable signal bandwidth is reduced with barbed posts. At the same time, the absence of barbed post structure might suggest that the fitting integrity of axially compressed connectors is compromised. The seal design of our invention is designed, in part, to ameliorate the latter potential problem.